Silver halide-based photography has conventionally been most widely used since the photographic characteristics of silver halide systems, such as sensitivity, gradation control, etc., are superior to those of other conventional photographic systems, such as electrophotography or the diazo process.
Recently, an improved photographic technique has been developed capable of simply and rapidly forming an image, in which development of a silver halide photographic material is carried out using a dye process under heat instead of a conventional wet process using a developing agent or the like.
Photographic materials for heat development using silver halides are well known in this technical field, and various photographic materials for heat development and processes are described, for example, in Bases of Photographic Industry, pp. 553-555 (Corona Publishing, 1979); Image Information, p. 40 (April, 1978); Nebletts Handbook of Photography and Reprography, pp. 32 and 33 (7th Ed., Van Nortrand Reinhold Company); U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075, British Pat. Nos. 1,131,108 and 1,167,777, and Research Disclosure (June, 1978), pp. 9-15 (RD-17029).
Several processes have been proposed for formation of color images by heat development. For instance, U.S. Pat. Nos. 3,531,286, 3,761,270 and 4,021,240, Belgian Pat. No. 802,519 and Research Disclosure (September, 1975), pp. 31-32 describe processes for formation of color images by combination of an oxidized developing agent and a coupler and various kinds of developing agents which may be used.
Research Disclosure (May, 1978), pp. 54-58 (RD-16966) describes a process where a nitrogen-containing heterocyclic group is introduced in a dye to form a silver salt and the formed dye is released by heat development.
Research Disclosure (April, 1976), pp. 30-32 (RD-14433) and (December, 1976), pp. 14-15 (RD-15227) and U.S. Pat. No. 4,235,957 describe a heat-sensitive silver dye bleaching process for formation of positive color images, and various methods for bleaching useful dyes.
U.S. Pat. Nos. 3,985,565 and 4,022,617 describe a process for formation of a color image by utilizing a leuco dye.
However, the known processes for formation of color images have the disadvantage that the color images formed are apt to discolor or white background is apt to color due to coexisting silver halide, silver complex, developing agent, etc., during preservation for a long period of time. Other color image formation processes by heat development have been proposed in order to overcome this defect, e.g., those described in Japanese Patent Application (OPI) Nos. 179840/82 (corresponding to U.S. Pat. No. 4,463,079), 186774/82 (corresponding to U.S. Pat. No. 4,474,867), 198458/82 (corresponding to U.S. Pat. No. 4,478,927), 207250/82 (corresponding to U.S. Pat. No. 4,507,380), 58543/83 (corresponding to U.S. Pat. No. 4,500,626), 79247/83 (corresponding to U.S. Pat. No. 4,483,914), 116537/83 (corresponding to U.S. Pat. No. 4,439,513), 149046/83, 48764/84, 65839/84 (corresponding to European Patent Application No. 106,211A), 71046/84 (corresponding to European Patent Application No. 106,357A), 87450/84, 88730/84 and 164551/84 (corresponding to European Patent Application No. 121,765A) (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
These publications describe a dye-transfer process where a diffusible dye is formed or released when a light-sensitive silver halide and/or organic silver salt is reduced to silver by heat development in correspondence or countercorrespondence with the reduction reaction, and the diffusible dye is transferred to a dye fixing material.
In such dye-transfer processes, in general, a small amount of water is applied to a dye fixing material to swell the material and the swollen dye fixing material is then closely attached to a diffusible dye-containing material and heated to transfer the dye to the dye fixing material. Accordingly, if the amount of water applied to the dye fixing material is too small, a long period of time is required for the dye-transferring operation, often resulting in the appearance of transferred dye mottles. However, if the amount of water applied is increased in order to shorten the time for the dye-transferring operation, it is apparent that the time required for water application will have to be long. On the other hand, if a dye fixing material is swollen with water and then directly attached to a photographic material, without removing excess water existing on the surface of the dye fixing material with a roller or the like, the transferred dye will often bleed out on the surface of the material, resulting in decreased sharpness of the formed color image, although a color image of high density may be obtained in a relatively short period of time.
In a dye-transfer process, as mentioned above, the transferred color image often locally bleeds out, since the water-swollen layer in the dye fixing material is often in an unstable state during the dye-transferring operation. In order to overcome this problem, Japanese Patent Application (OPI) No. 164551/84 (corresponding to European Patent Application No. 121,765A) has proposed that the amount of water applied to the dye fixing material in the dye-transfer procedure is restricted to an amount equal to (the weight of water corresponding to the maximum swollen volume of the total coated layers of both the diffusible dye-containing photographic material and the dye fixing material) minus (the weight of the total coated layers) or less. According to this method, however, a long period of time is required for the coated layer of the dye fixing material to absorb a sufficient amount of water which is necessary in order to attain a sufficiently rapid dye-transferring with reduced mottle, using this amount of water.
On the other hand, Japanese Patent Application (OPI) No. 165056/84 (corresponding to U.S. patent Ser. No. 588,416, filed on Aug. 12, 1984, which already was abandoned) describes that various hydrophilic polymers can be used alone or in combination of two or more of them as a binder for dye fixing materials, but it does not specifically describe that a cross-linked hydrophilic polymer and a non-cross-linked hydrophilic polymer are used in combination with each other.
Therefore, no satisfactory dye-transfer process could be realized as yet.